Manipulating the frequency and bandwidth of non-classical light is essential for implementing frequency-coded/multiplexed quantum computation, communication and networking protocols and bridging spectral mismatch between different quantum systems. However, quantum spectral control requires strong nonlinearity mediated by light, microwaves or acoustics, which is challenging to achieve with high efficiency, low noise and on an integrated chip.

Applied scientists and engineers at Harvard’s John A. Paulson School of Engineering and Applied Sciences (SEAS) recently developed an integrated electro-optical modulator that effectively modifies the frequency and bandwidth of individual photons. Quantum networks and more advanced quantum computing could also benefit from the device.

A photon is usually converted from one color to another by injecting it into a crystal with a powerful laser beam; however, this method is usually ineffective and loud. A more effective technique is phase modulation, which speeds up or slows down the oscillation of a photon wave to change the photon’s frequency. However, incorporating an electro-optical phase modulator onto a chip has proved challenging.

Thin-film lithium niobate could be suitable for such applications.

Marko Lončar, the Tiantsai Lin Professor of Electrical Engineering at SEAS and senior author of the study, said: “In our work, we applied a new modulator design to thin-film lithium niobate that significantly improved the performance of the device. This integrated modulator achieved record high terahertz frequency shifts of a few photons.”

Using the same modulator as a time lens, the team changed the spectral shape of a photon from thick to lean.

Di Zhu, the first author of the article, said: “Our device is much more compact and energy efficient than the traditional bulk device. It can be integrated with various classical and quantum devices on the same chip to achieve more advanced quantum light control.”

Scientists also want to use the device to control the frequency and bandwidth of quantum transmitters for applications in quantum networks.

Magazine reference:

  1. Zhu, D., Chen, C., Yu, M. et al. Spectral control of non-classical light pulses using an integrated thin-film lithium niobate modulator. Light Sci Appl 11, 327 (2022). DOI: 10.1038/s41377-022-01029-7